The present invention relates to an arrangement for automatic drift compensation in a gas analyzer. A radiation source radiates through the gas to be analyzed and onto a radiation detector which is connected to a circuit for forming an amplified output signal corresponding to the output of the radiation detector and hence corresponding to the gas concentration. Rapid and accurate gas analyzers are required for medical purposes, e.g., for respirator treatments and lung function analysis.
During respirator treatments, the correct treatment is determined on the basis of the CO.sub.2 content of the gas exhaled by the patient. It is, therefore, necessary to determine the CO.sub.2 content quickly and accurately. A photometric measuring method is the most expedient method. Here the transfer properties of the gas exhaled by the patient for the rays of a light source are used to determine the CO.sub.2 content.
It is already known in the art that by means of a suction pump, gas samples can be taken continuously or intermittently from the gas mixture exhaled by a patient and the samples may be delivered to a special measuring chamber for analysis, to determine the CO.sub.2 content, for example. Due to the fact that CO.sub.2 is mixed with other gases, and to the delay caused by the hose connection between the respirator and the measuring chamber, there develops a deformation of the recorded CO.sub.2 curve. As a result, the phase relation between the CO.sub.2 curve and the actual gas flow curve in the respirator hose cannot be accurately established. It is, therefore, more advantageous to use a radiation source of suitable spectral distribution and to direct the radiation coming from the radiation source directly to the gas flowing to or away from the patient. It is preferable to direct it to a detector via a radiation interrupter and a suitable filter.
Due to the low signal levels requiring the use of amplifiers with large gains, and because of interferences stemming from the varying radiation intensity of the radiation source and from dirt deposits on the glass terminating the gas line, problems arise with respect to drift compensation.
It is, therefore, the object of the present invention to provide an arrangement in which automatic drift compensation takes place.
Another object of the present invention is to provide an arrangement of the foregoing character which may be economically fabricated and maintained in service.
A further object of the present invention is to provide an arrangement, as described, which has a substantially long operating life.